Component with internal damping

ABSTRACT

A method of manufacturing a component such as a gas turbine fan blade. The method comprises: disposing a plurality of webs between a plurality of panels; and deforming the panels and the webs by applying internal pressure between the panels, thereby forming a series of internal cavities ( 15 ) partitioned by the webs ( 20 - 22 ). Weakened regions ( 30   a , 30   b , 30   c ) are formed in the webs which open to form holes ( 30 ) in the webs ( 20 - 22 ) during the deformation step. A damping material ( 17 ) is introduced into at least one of the cavities ( 15 ) whereby it flows from the cavity into the other cavities via the holes in the webs.

FIELD OF THE INVENTION

The present invention relates to a component with internal damping, amethod of manufacturing such a component, and a precursor assembly forforming such a component. The invention is particularly, although notexclusively, concerned with components for use in gas turbine engines,for example fan blades.

BACKGROUND OF THE INVENTION

In US 2004/0191069, a gas turbine blade is manufactured by asuperplastic forming and diffusion bonding technique which results in ahollow blade, ie a blade having at least one internal cavity. A pair ofpanel precursors are laid in face-to-face contact with a membraneprecursor. A predetermined pattern of stop-off material is applied tothe panels. The precursors are diffusion bonded together, except wherethis is prevented by the stop-off material. Subsequently, internalpressure is created between the panels, causing the panels and membraneto deform superplastically to form a warren girder structure, withcavities in the regions where diffusion bonding was prevented by thestop-off material.

The blade is subject to vibration induced by flutter and distortions inthe gas flow over the blades. US 2004/0191069 A1 describes a method ofdamping such vibrations by coating the inner surface of the blade with asuitable damping material.

In order to achieve damping, a degree of relative movement is requiredbetween the panels and the damping material. A problem with thearrangement of US 2004/0191069 A1 is that the warren girder structure istoo stiff to permit a significant degree of such relative movement.Furthermore, the warren girder structure is relatively heavy.

SUMMARY OF THE INVENTION

A first aspect of the invention provides a method of manufacturing acomponent, the method comprising: disposing a plurality of webs betweena plurality of panels; and deforming the panels and the webs by applyinginternal pressure between the panels, thereby forming a series ofinternal cavities partitioned by the webs, characterised in that themethod further comprises:

-   -   forming weakened regions in the webs which open to form holes in        the webs during the deformation step; and    -   introducing a damping material into at least one of the cavities        whereby it flows into the other cavities via the holes in the        webs.

A second aspect of the invention provides a component comprising:

-   -   a plurality of panels; and    -   a plurality of webs extending between the panels and        partitioning the component into a plurality of internal        cavities,    -   characterised in that the component further comprises:    -   an array of holes formed in each web; and    -   a damping material substantially filling the internal cavities.

The component is preferably manufactured by the method of the firstaspect of the invention.

The following comments apply to both the first and second aspects of theinvention.

The webs may be comprise separate and distinct web members. Howeverpreferably the webs comprise spaced-apart web regions of a membraneprecursor, and the membrane precursor is bonded between the web regionsto an opposed pair of the panels.

Stop-off material may be applied to prevent or minimise bonding betweenthe web regions of the membrane precursor and the opposed pair ofpanels. This material may be applied to the web regions and/or to theopposed pair of panels. Typically the stop-off material is applied in astriped pattern, the spaces between adjacent stripes on one side of themembrane precursor being disposed opposite a stripe on the other side ofthe membrane precursor, whereby the webs forms a warren girder structurewithin the component.

The component may be any component which is subject to vibration orimpact when in use, for example a rotating blade such as a fan blade ofa gas turbine engine, a stationary vane such as an outlet guide vane ofa gas turbine engine, or a containment ring which surrounds a rotatingcomponent and is able to withstand impact in the event of catastrophicfailure of the rotating component.

In a specific embodiment in accordance with the present invention, thecomponent is a component for a gas turbine engine, for example a rotorblade such as a fan blade. Such a component is commonly manufacturedprincipally from a metallic material, for example a titanium alloy.

Where the component is a rotating component, then the webs preferablyextend in a radial direction so that they can carry radial load when inuse, although in general the webs may extend in any direction.

The damping material may be any flowable material with suitable dampingproperties. In the context of this invention “damping material” means amaterial which dissipates strain energy, for example as heat, to asignificant extent, by which is meant an extent greater than the energydissipation of the principal material from which the component isformed. Preferably the damping material is a visco-elastic material.Typically the damping material is hardened after it has flowed into thecavities. For example the damping material may be a resin which isheated to cure the resin. Alternatively the material may be athermoplastic material which is heated before being injected into thecomponent, and hardens on cooling.

The damping material may be injected into more than one of the cavities.However, a problem with this is that more than one of the cavities mustbe weakened with an inlet port, and more than one injection system isrequired. Therefore more preferably the material is introduced into onlyone of the cavities, preferably via only one port, and flows from thatcavity into all other cavities.

The weakened regions may be formed by cutting the webs, typicallythrough the full thickness of the web, or machining them in any otherway.

During the machining process, material may be removed from the webs toform open holes, or the webs may be machined without removing material(for instance by cutting slits in the web).

A third aspect of the invention provides a precursor assembly forforming a component, the assembly comprising: a plurality of panelprecursors; and a membrane precursor disposed between the panelprecursors, characterised in that the assembly further comprises aplurality of weakened regions formed in a plurality of spaced-apart webregions of the membrane precursor.

The precursor assembly is suitable for use in manufacturing a componentby the method of the first aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theaccompanying drawings, in which:

FIG. 1 is a sectional view taken through a fan blade of a gas turbineengine;

FIG. 2 is an enlarged view of the region A in FIG. 1;

FIG. 3 is a schematic perspective view of a precursor assembly;

FIG. 4 is a plan view of a web region of the flat membrane precursoraccording to a first example;

FIG. 5 is a plan view of a web region of the flat membrane precursoraccording to a second example;

FIG. 6 is a plan view of a web region of the flat membrane precursoraccording to a third example;

FIG. 7 is a perspective view of part of the warren girder structure; and

FIG. 8 shows six alternative hole shapes and configurations.

DETAILED DESCRIPTION OF EMBODIMENT(S)

The fan blade shown in FIG. 1 comprises outer panels 2,4 between which awarren girder structure 6 is disposed. The panels 2, 4 and the warrengirder structure 6 are made from a titanium alloy. The panels 2 and 4are diffusion bonded to each other at the leading and trailing edges 8,10 of the blade, and to the warren girder structure 6 at contact regions12, so that the warren girder structure 6 provides a plurality ofpartitions extending across the interior of the blade.

The blade shown in FIGS. 1 and 2 is formed from a precursor assemblyshown in FIG. 3. The precursor assembly comprises an opposed pair ofpanel precursors 2 a, 4 a (which eventually form the panels 2,4); and amembrane precursor 6a (which eventually forms the warren girderstructure 6) disposed between the panel precursors. These precursors areinitially flat.

A series of stripes 14 of stop-off material, for example yttria, areapplied to the inner surface of the panel precursors, between thecontact regions 12. The stop-off material may, for example be applied bya silk screen printing process.

It will be appreciated from FIG. 2 that the stop-off stripes 14 on thepanels 2 and 4 (and consequently on their precursors) are offset withrespect to each other, so that the spaces between the stop-off stripes14 on one of the panels are disposed opposite the stop-off stripes 14 onthe other panel. The spacing between adjacent stripes 14 is narrowerthan the stripes themselves, with the result that the oppositely facingstripes 14 slightly overlap one another.

The precursors are pressed together at high pressure and temperature sothat diffusion bonds are created between contacting metal-to-metalregions corresponding to the contact regions 12 in FIG. 2. The yttriastop-off material prevents full bonding between the stripes 14 and themembrane precursor 6 a.

When bonding has been achieved, the bonded precursor assembly is heatedto a temperature at which the assembly can be hot formed into a desiredconfiguration in which, for example, the assembly has an arcuatecross-section with a twist between the ends of the assembly,approximating to a desired blade profile.

Subsequently, the bonded and hot formed precursor assembly is heated toa temperature at which superplastic deformation of the elements of theassembly can occur, and the assembly is internally pressurised by theintroduction of high pressure inert gas, such as argon. An inlet port isprovided in a wall of the precursor assembly and a delivery tube iswelded onto the inlet port to define an inlet passage to the interior ofthe assembly. The delivery tube provides a sealed passage for the highpressure inert gas and prevents contamination of the inert gas withoxygen, thus preventing oxidation of the material of the. precursorassembly. The high pressure gas forces the panels 2 and 4 apart fromeach other between their leading and trailing edges. Since the membraneprecursor 6a is diffusion bonded at staggered intervals to the panels 2and 4, but not bonded where the yttria stop-off material is present, themembrane will superplastically deform into the configuration shown inFIGS. 1 and 2. After super plastic deformation has taken place the pipeis removed and the inlet port is blocked up. In an alternativeembodiment the inlet port can also be used for the delivery of avisco-elastic material 17, as described below.

FIGS. 4-6 are plan views of a web region 22 a of the flat membraneprecursor 6 a according to three examples, with the web region 22 a(that is, the part of the membrane that will eventually form the web 22)bounded by a pair of dash-dot lines and the radial direction beingindicated by an arrow R. In each case the web region of the membrane iscut to form a series of weakened regions. Note that no weakened regionsare formed outside the web region.

In the example of FIG. 4 the weakened regions are closed slits 30 a. Inthe example of FIG. 5 the weakened regions are open holes 30 b. In theexample of FIG. 6 the weakened regions are series of groups 30 c ofsmall slits. Note that the slits in FIGS. 4 and 6 are formed by cuttingthe membrane without the removal of any material, whereas the holes 30 bin FIG. 5 are formed by removing material.

FIG. 7 is a perspective view of the membrane 6 after the superplasticdeformation step, with the radial direction being indicated by an arrowR. As shown in FIG. 7, the membrane comprises a series of webs 20-22which extend between the panels 2,4, and a series of feet 23-25 bondedto the panels 2,4 in the contact regions 12. The webs 20-22 and feet23-25 extend radially along the full length of the blade, or over apatched area of the blade, thereby partitioning the hollow interior ofthe blade into a series of internal cavities 15. Note that forillustrative purposes only a small portion of the full radial length ofthe membrane is shown in FIG. 7.

During the superplastic deformation step, the weakened regions open upto form a series of holes 30 as shown in FIG. 7. Note that although noholes are shown in the webs 20,21, holes will be formed in thesewebs—either in the radial location shown in FIG. 7 or at other radiallocations along the length of the blade.

The weakened regions need to be constructed in such a way that the webdoes not tear during the subsequent forming steps. The holes in the websmay be regular or irregular shapes, and the weakened regions may besized and shaped such that after the deformation process they open up toform a different and more beneficial shape (such as a flattened hexagonbecoming a regular hexagon). A number of different arrangements andshapes of hole are possible, and six variants are shown in FIG. 8.

After the superplastic deformation step, a liquid visco-elastic material17 is injected into the hollow interior of the blade via a port 16 asshown in FIG. 2. By way of non limiting example, a suitablevisco-elastic material is a Huntsman™ single or two part syntactic foam.Alternatively a thermoplastic spray formed damper such as AIREX R63® asmanufactured by Impag may be used. Note that the injection apparatus isomitted from the Figures for purposes of clarity. However, positioningof the filler may be aided by a guide tube (not shown) inserted throughthe port 16. Additionally the position of the filler can be influencedby orientating the blade such that the filler will flow to a desiredlocation in the blade under gravity.

Upon injection, the material first flows into the cavity 15 next to theport 16 as shown in FIG. 2, then flows into the other cavities via theholes in the webs 20-22. At the end of the injection process, the hollowblade is substantially filled with liquid visco-elastic material, whichsubsequently hardens.

The internal surfaces of the blade cavity (ie the internal surfaces ofthe panels 2 and 4) may be cleaned by an acid etch technique prior tothe injection of the filler material, thereby increasing the bondstrength between the filler and the panel wall surfaces. The resultingstructure is consequently that of a hollow component filled withvisco-elastic damping material. The component therefore exhibits areduction in the amplitude of vibration when subjected to excitation,for example by flow conditions around the blade. The reduced amplitudeof vibration thus reduces the tendency of the blades to fail under highcycle fatigue conditions.

Furthermore, since the damping material is contained within the blade,it is not exposed to gas flow over the blade, nor to foreign objectsstriking the blade.

Furthermore, the outer surface finish of the blade is not influenced bythe presence of damping material and so can be optimised to provide thedesired aerodynamic characteristics of the blade.

The webs 20-22 are capable of carrying a radial load, hold the panelstogether to prevent panting of the blade or delamination of the panelsduring high centrifugal loads, and also bind the visco-elastic dampingmaterial in place.

The holes in the webs reduce the stiffness of the webs, enablingrelative movement between the blade and the visco-elastic dampingmaterial. This enables the material to damp vibrations more efficiently,compared with an arrangement in which the webs have no holes. At thesame time, the holes enable the damping material to flow between theinternal cavities 15 and substantially fill the blade. Also, the holesreduce the total weight of the warren girder structure.

Although the invention has been described above with reference to one ormore preferred embodiments, it will be appreciated that various changesor modifications may be made without departing from the scope of theinvention as defined in the appended claims.

1. A method of manufacturing a component, the method comprising:disposing a plurality of webs between a plurality of panels; anddeforming the panels and the webs by applying internal pressure betweenthe panels, thereby forming a series of internal cavities partitioned bythe webs, characterised in that the method further comprises: formingweakened regions in the webs which open to form holes in the webs duringthe deformation step; and introducing a damping material into at leastone of the cavities whereby it flows into the other cavities via theholes in the webs.
 2. The method of claim 1, wherein the webs aredeformed superplastically.
 3. The method of claim 1, wherein the webscomprise spaced-apart web regions of a membrane precursor, and themethod further comprises bonding the membrane precursor between the webregions to an opposed pair of the panels.
 4. The method of claim 3,further comprising applying a stop-off material to prevent or minimisebonding between the web regions of the membrane precursor and theopposed pair of panels.
 5. The method of claim 4, wherein the stop-offmaterial is applied to the opposed pair of panels.
 6. The method ofclaim 4, wherein the stop-off material is applied in a striped pattern,the spaces between adjacent stripes on one side of the membraneprecursor being disposed opposite a stripe on the other side of themembrane precursor, whereby the webs forms a warren girder structurewithin the component.
 7. The method of any claim 1, wherein thecomponent is a component for a gas turbine engine.
 8. The method ofclaim 1 wherein the component rotates when in use, and the webs extendin a radial direction.
 9. The method of claim 1 further comprisinghardening the damping material after it has flowed into the cavities.10. The method of claim 1 wherein the damping material is introducedinto only one of the cavities, and flows from that cavity into all othercavities.
 11. The method of claim 10 wherein the damping material isintroduced into the one cavity via only one port.
 12. The method ofclaim 1 wherein the weakened regions are formed by cutting the webs. 13.The method of claim 1 wherein the weakened regions are formed byremoving material from the webs.
 14. The method of claim 1 wherein theweakened regions are formed without removing material from the webs. 15.A precursor assembly for forming a component, the assembly comprising: aplurality of panel precursors; and a membrane precursor disposed betweenthe panel precursors, characterised in that the assembly furthercomprises a plurality of weakened regions formed in a plurality ofspaced-apart web regions of the membrane precursor.
 16. The assembly ofclaim 15 wherein the membrane precursor is bonded between the webregions to an opposed pair of the panel precursors.
 17. The assembly ofclaim 16, further comprising a stop-off material disposed between theweb regions to prevent or minimise bonding between the membraneprecursor and an opposed pair of the panels.
 18. The assembly of claim17, wherein the stop-off material is applied in a striped pattern, thespaces between adjacent stripes on one side of the membrane precursorbeing disposed opposite a stripe on the other side of the membraneprecursor.
 19. A component comprising: a plurality of panels; and aplurality of webs extending between the panels and partitioning thecomponent into a plurality of internal cavities, characterised in thatthe component further comprises: an array of holes formed in each web;and a damping material substantially filling the internal cavities.